Turbine engine combustion chamber liners may be made of multiple, axially successive louvers circumscribing a combustion chamber centerline. A typical louver has a forward panel, an aft panel and a short bulkhead that projects radially to connect the forward and aft panels to each other. A louver assembly comprises a forward louver and an aft louver arranged so that the aft panel of the forward louver nests radially inside the forward panel of the aft louver. The aft panel of the forward louver also extends axially past the connecting bulkhead of the aft louver to define a lip. A weld joint extends circumferentially to join the forward panel of the aft louver to the aft panel of the forward louver. The lips of certain louvers, particularly louvers that are not near the axially forward end of the liner, may include a series of circumferentially distributed slots. These lip slots help relieve thermal stresses that could cause cracks in the lips of those louvers. Experience shows that such lip slots are unnecessary in the louvers residing closer to the forward end of the liner.
Turbine engine manufacturers strive to minimize undesirable exhaust emissions arising from combustion of a fuel and air mixture in the combustion chamber. U.S. Pat. Nos. 6,101,814 and 6,715,292 (the contents of both of which are incorporated herein by reference) describe a combustor liner and associated fuel injector that produce considerably reduced emissions in comparison to early generation combustion liners. Throughout this specification the low emissions liner described in the aforementioned patents will be referred to as an intermediate generation liner; the predecessor to the intermediate generation liner will be referred to as an early generation liner. Experience reveals that a louver near the forward end of the early generation liner, specifically the second louver L2, does not require lip slots in order to resist cracking of the lip. Similarly, no lip slots are required in the second louver L2 of the intermediate generation liner to resist cracking of the lip. However in the intermediate generation liner, the forward panel of the axially adjacent aft louver (louver L3) exhibits susceptibility to cracking in the immediate vicinity of the weld joint that secures the louvers to each other. The cracking is believed to arise because a portion of forward louver L2 that is relatively hot during engine operation nests radially inside of a portion of aft louver L3 that is relatively cool during engine operation. The relatively cool portion of aft louver L3 is unable to withstand the cyclic, thermally induced radial expansion (and contraction) of the relatively hot portion of forward louver L2. The cracking is undesirable because it requires more frequent inspections than would otherwise be necessary and may also require replacement or reconditioning of an otherwise serviceable liner or its louvers.
What is needed is a combustor liner louver assembly whose louvers exhibit improved forward panel crack resistance.